Any vehicle that compensates considerably for irregularities in the road and hence in the consequent shifts in the position of the axle and accordingly exposes its passengers to only a low level of motion is characterized as comfortable. The motion induced in the passengers is accordingly generally considered the measure of comfort within the context of vibration.
European Exposure 270 893 discloses a mechanism for actively controlling a motor-vehicle chassis. The level is controlled in conjunction with associated active or semiactive attenuators plus passive spring or attenuating mechanisms. The device, however, is very complicated and does not represent a cost-effective solution. Furthermore, the number of components is very large, making the whole system likely to malfunction. A principle of controlling semiactive chassis called the skyhook principle is known. In accordance with this principle, if Va represents the vertical body velocity and Vr the vertical wheel velocity, a bypass valve is closed when Va.multidot.(Va-Vr).ltoreq., subsequent to which the attenuator operates with a hard characteristic.
When Va.multidot.(Va-Vr)&lt;, the bypass valve is opened, subsequent to which the vibration attenuator will operate with a soft characteristic. Vertical body velocity Va is determined by a sensor that integrates body acceleration a.sub.a. This method of determination is not only very complicated but does not calculate body velocity precisely enough for the subsequent controlling process.